originally when the transmission was assembled to the engine the numbers were stamped into the trans case above the inspection cover, this was done at the Rouge plant, this assembly was then sent to the various final assembly plants where it was placed into a frame and THEN the frame was stamped with these numbers suppossedly in at least 3 locations, frame rail by engine, frame rail under drivers door and rear spring crossmember pass. side. As long as it had a V8 it was done this way until the 99T was used on 100 hp trucks in 1940